Unsaturated fats, 439 Table

The fat from an animal or plant is a mixture of different fat molecules having various degrees of unsaturation. Fat molecules containing only one carbon-carbon double bond per fatty acid chain are monounsaturated. Those containing more than one double bond per fatty acid chain wee polyunsaturated. Table 13.1 on page 442 shows the percentage of saturated, monounsaturated, and polyunsaturated fats in a number of widely used dietary fats. 

Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end. They can be classified on the basis of the length of the hydrocarbon chain (Table 2.2) and whether there are any double bonds. Trivial names of fatty acids such as butyric, lauric, oleic and palmitic acids are in common use in the food industry. A form of short-hand is used to refer to triglycerides where POS is palmitic, oleic, stearic. If the chain length is the same an unsaturated fat will always have a lower melting point. Another classification of fats that is used is in terms of the degree of unsaturation of the fatty acids. Saturated fats are fats without any double bonds. Many animal fats are saturated, but some vegetable fats, e.g. coconut oil, are saturated also. Mono-unsaturated fats include oils like olive oil but also some partially hydrogenated fats. Polyunsaturated fats have many double bonds and include sunflower oil. Because they are... 

Most natural triacylglycerols do not have a random distribution of fatty acids on the glycerol backbone. In plant oils, unsaturated acids predominate at the sn-2 position, with more saturated acids at sn-l and sn-3. The distribution of fatty acids at the sn-l and sn-3 positions is often similar, although not identical. However, a random distribution between these two positions is often assumed as full stereospecific analysis is a time-consuming specialist procedure. In animal fats, the type of fatty acid predominating at the sn-2 position is more variable for example, palmitate may be selectively incorporated as well as unsaturated acids (Table 5). 

The flash point defines the temperature at which the decomposition products formed from frying oils can be ignited. This temperature ranges from 275°C to 330°C for different oils and fats (Table 13). An increase in the content of unsaturated fatty acids usually decreases the flash and smoke points (60). 

The roasted red pepper seed oil contained an extremely high concentration of linoleic acid, approximately 74%, and a high total unsaturated fat level (Table 6) (37). The fatty acid profile was very similar to that of both goldenberry seed (Physalis peruviana L.) and safflower oils (36). The iodine value of roasted red pepper seed oil was determined to be 137-g iodine/lOO-g oil.This shows that there is a high degree of unsaturation in the oil. Oxidative stabilities of the roasted red... 

A study on diet and colon cancer was reported by W. Willett s group (Willett et at., 1990) (Table 11.3). The study examined various components of the diet, such as fiber, fat, and meat. The fiber component was divid into cereal fiber and fruit fiber. The fat component was divided into meat fat, dairy fat, saturated fat, and unsaturated fat. The meat component was divided into beef, pork, and lamb, and into rare versus well-done Styles of cooking. The body mass index, as defined in the Obesity chapter, was also recorded. The study was part of the Nurses Health Study Cohort, which was inibated in 1976 and involved 121,700 female nurses. Every 2 years, the nurses filled in a questionnaire that asked about various risk factors for disease. The questionnaire asked, for example, about 61 foods and their frequency In the diet. The foods were chosen to allow epidemiologists to make broad statements regarding the component nutrients. 

Experimental Diets. The three experimental diets used were based on the AIN-93 (35) formulation with several modifications to obtain the extremely low n-3 fatty acid level required in this study (Table 1). The custom-pelleted diets were obtained commercially and employed a cold pelleting process to preserve unsaturated fats (Dyets, Bethlehem, PA). The dependent variable in the two artificially reared groups was the substitution of a-linolenic acid ethyl ester for oleic acid ethyl ester in the n-3 Adq diet. The maternal diet contained a fatty acid composition similar to that of the n-3 Adq diet but made up with a mixture of safflower and flax oils due to the greater quantity of diet to be consumed. All three diets contained 10 wt% fat and had a similar Unoleic acid content. The rats were fed these diets until they were sacrificed. 

Table 22.1 Content of unsaturated fatly acids in rubber seed oil (RSO)...

TABLE III. Effects of Unsaturated Fats on Bile Acid Metabolism in Man... 

The use of NIR reflectance has gained considerable interest for process analysis in the food, pharmaceutical, petrochemical, and other chemical industries. This method requires little or no sample preparation and involves measurement of the reflectance of a liquid or solid sample relative to that of a standard in the same wavelength series. As illustrated in Table 3, process NIR has gained considerable use for moisture determination in coal, cosmetics, and detergent powders, as well as for protein contents of cereal and grain, and hydrogenation of unsaturated fats and oils. 

The optimum pH for meat depends on the purpose for which it is intended. Fresh meat should be at the upper end of the normal pH range if it is to be preserved by freezing, since the reaction between myoglobin and unsaturated fat is inhibited in this range (see table V) and both discoloration and also fat oxidation are retarded. In addition, drip losses are minimized (Sair and Cook, 1938). 

Esterification of glycerol with saturated short chain fatty acids and unsaturated short-and medium chain fatty acids usuaUy results in (at room temperature) liquid oils longer fatty acids give hard fats. Table 23.9 shows several examples of natural and synthetic oils and fats. 

Numerous experiments with mice and rats have shown that animals on high fat diets develop mammary tumors more readily than similarly treated controls on low fat diets (Tannenbaum Silverstone, 1957 Tannenbaum, 1959 Carroll Khor, 1975 Carroll, 1975). In our own studies on rats treated with 7,12-dimethylbenz(a)anthracene (DMBA), unsaturated fats increased tumor yields more than saturated fats (Table 1). However, there did not seem to be a direct correlation with essential fatty acid content since lard and olive oil were about as effective as corn oil and soybean oil, although the latter are much richer in linoleic acid (Carroll Khor, 1971). Dayton and Hashimoto (1976) reached a similar conclusion on the basis of their experiments with an oil rich in oleic acid produced by a mutant safflower. This oil was found to be as effective as normal high-linoleic safflower oil in stimulating development of mammary... 

In contrast to the composition of triacylglycerols found in beef fat (Table 3.13), lard contains fewer triacylglycerols of the type SSS and more of the types SUU, USU and UUU (S = saturated U = unsaturated fatty acid). As a consequence, lard melts at lower temperatures and over a range of temperatures rather than sharply at a single temperature, and its shelf life is not particularly long. In comparison with beef, pig depot fat... 

Table 8. Unsaturated Acids as % of Total Acids of Milk Fat ...

Generally, unsaturated compounds, eg, alkenes and natural fats and their derivatives, are much more reactive toward sulfur than alkanes. Sulfur reacts with unsaturated compounds at temperatures of 120—215°C, forming products that are usually dark and often viscous cross-linked mixtures of dithiole-3-thiones (eq. 4) (2) and sulfides (Table 1) (3). 

In all of the workshops, but especially in the FAT and Exposure Assessment workshops, the need for better understanding and model representation of soil systems, including both unsaturated and saturated zones, was evident. This included the entire range of processes shown in Table II, i.e., transport, chemical and biological transformations, and intermedia transfers by sorption/desorption and volatilization. In fact, the Exposure Assessment workshop (Level II) listed biological degradation processes as a major research priority for both soil and water systems, since current understanding in both systems must be improved for site-specific assessments. 

Fatty acids can then be classified by their degree of unsaturation as well as their chain length. Thus, fatty acids are either saturated if they have no double bonds or unsaturated. Unsaturated fatty acids are further subdivided into monounsaturated diunsaturated and so on. Fatty acids with many double bonds are classed as polyunsaturated. Table 3 gives the approximate fatty acid compositions of several fats and oils, Table 4 lists the unsaturated fatty acids found in milk (note the very wide diversity). 

Polyunsaturated fatty acids are characterized by a large number of C = C double bonds in their hydrocarbon chain. Stearic acid has no C = C double bonds and therefore is not unsaturated, let alone polyunsaturated. But eleostearic acid has three C = C double bonds and thus is polyunsaturated. Polyunsaturated fatty acids are recommended in dietary programs since saturated fats are linked to a high incidence of heart disease. Of the lipids listed in Table 28-2, safflower oil has the highest percentage of unsaturated fatty acids, predominately linoleic acid, an unsaturated fatty acid with two C=C bonds. 

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